CLASS REPTILIA 



533 



and appendages. The air is thus pumped into the lungs or else 

 swallowed. 



Many aquatic turtles possess a pair of thin-walled sacs (Fig. 

 442, cc f ), one on either side of the cloaca (cl), which are alternately 

 filled with water and emptied through the anus. They have 

 walls plentifully supplied with blood-vessels, and act as auxiliary 

 breathing organs (compare sea-cucumber, p. 206, and nymph 

 of dragon-fly, p. 339). 



The Urinogenital Organs (Fig. 442). Excretion is carried 

 on by the two kidneys (r). Their secretions pass through the 

 ureters (u) into the cloaca (cl), are stored in the urinary bladder 

 (v), and then make their exit (ug) through the anus. 



The sexes are separate. The male organs are a pair of testes 

 (t) and a pair of vasa deferentia (e) through which the spermat- 

 ozoa pass to the grooved copulatory organ, or penis (p), at- 

 tached to the front wall of the cloaca (cl). The female organs 

 are a pair of ovaries and a 

 pair of oviducts ; the latter 

 open into the cloaca. 



Turtles are oviparous. 

 The eggs, which are white, 

 round or oval, and covered 

 by a more or less hardened FlG 443 _ side view of brain of a turtle 



shell, are laid in the ground /, olfactory nerve ; //, optic nerve ; //, hypo- 



. , ,1 physis; HH, cerebellum; Inf, infundibulum; 



' Lot, olfactory lobe; MH, optic lobe; NH, me- 



SUrface. dulla; R, spinal cord; VII, cerebral hemi- 



(From Davenport, after Wieders- 



The Nervous System. 



-The brain (Fig. 443) is 



more highly developed than in the AMPHIBIA. The cerebral 

 hemispheres (VH) are larger, and a distinction can be made 

 between the superficial gray layer and the central white medulla. 

 The cerebellum (HH) is also larger, indicating an increase in the 

 power of correlating movements. 



Sense-organs. The eye is small. It has a round pupil and 

 an iris which is usually dark in terrestrial forms, but often 



